1. Field of the Invention
The present invention relates generally to the embossing of sheet materials including thermoplastics and more particularly to a thermoplastic embossed sheet manufactured using an inline positive-driven embossing station.
2. Background
The need for embossed plastic materials has continued for some time and has had particular application in the development of products capable of safely containing and protecting valuable and collectible items during handling, inspection, buying, selling, storage, and transportation of such items. In the past, a wide variety of embossed plastic materials have been used in the construction of products such as protective containers for use in albums, carrying cases, and filing containers that are designed to hold such valuable and collectible items and objects. Such valuable and collectible items include, but are not limited to, coins, bottle tops, pogs, optical disks, magnetic disks, audio and video disks and tapes, stamps, jewelry, electronic chips or chip sets such as processors and memory chips and EPROMs, photographs, negatives, match books, and other similar items and objects.
Such protective containers often include two or more plastic sheets joined together to form a protective pocket within which an item may be inserted for storage and display. The shape of the pocket is designed to accommodate the type of item to be protected and stored. Often the plastic sheets are formed to have a generally rectangular shape of a size suitable for holding the item to be protected. The sheets are typically joined by adhesives, welds, staples, rivets, or other appropriate fastening means to form a seam along three sides leaving one side of the pocket open so that an item may be readily inserted and removed from the pocket. In some protective container products, one or more of the plastic sheets will be embossed with a three-dimensional preselected image or image pattern that is designed to improve the appearance and protective capability of the protective containers.
Most commonly, the images that are embossed or molded into plastic sheet materials have been formed, molded, embossed, imprinted, or impressed using any of a number of plastic finishing techniques including calendering, compression molding, cold forming, injection molding, thermoforming, and transfer molding. Typically, a combination of calendering and cold forming has been used to emboss a material as part of a larger manufacturing and assembly production line wherein the embossed plastic sheet material is directed into an assembly line which incorporates the embossed sheet into the protective container, sleeve, or container.
Such an embossing station is configured to mold, form, emboss, imprint, or impress an image pattern into a sheet of plastic material that is drawn from a roll. The impressed or embossed plastic material is then fed into a later stage of the manufacturing and assembly production line and the material is incorporated into a finished component or product. The embossing station usually includes a die press or a pair of rollers. The high-speed processing of plastic sheet material typically employs platen and die rollers to emboss the plastic sheet with the preselected image or image pattern. The die roller includes a die in the shape of the preselected image or a pattern of such dies. The platen roller may have a flat surface about its circumference or it may incorporate a recess or pattern of recesses corresponding with the embossing die or pattern of dies, respectively. During embossing, the portion of the plastic sheet material in contact with the die (or die and platen) is momentarily stretched into the three-dimensional shape of the preselected image or image pattern as the sheet passes through the rollers, thus impressing or forming the preselected image into the plastic sheet material.
Although many types of plastic embossing techniques have been employed to emboss an image pattern onto plastic sheet, a persistent problem has existed. After the stored object or item is removed from the protective container or page of protective containers, the embossed image typically fails to fully recover its original three-dimensional shape. Therefore, when the embossed protective container is reused, the embossed article cannot function as intended--to provide a cushioned surface to protect the valuable collectible or article. Moreover, any aesthetic value attributable to the embossed image is lost.
The currently known embossed images in widely used materials suffer from dimensional instability in that the embossed image usually deteriorates rapidly after embossing because the plastic material naturally and gradually relaxes so that the image pattern flattens considerably.
In addition to the natural relaxation of the embossed plastic material, the image further deteriorates and flattens when it is used in a protective container for storage or transportation of an object. The additional deterioration results from the compressive and tensile effects experienced by the plastic material when an object is inserted into the pocket of the protective container. The pocket and therefore the joined plastic sheets are necessarily distended slightly from their natural orientation and the plastic sheets experience a tension in the plane of the sheet material. In response to such tension, the plastic sheet material is pressed against the object in the pocket. In other words, the embossed image is stretched in the planar direction of the sheet material and the image is pressed flat against the object. These multiple sources of deterioration serve to significantly and undesirably reduce the aesthetic value and protective function of the embossed image or image pattern.
What has been needed but previously unavailable is an improved, inexpensive, durable, and long-lasting embossed plastic sheet material and a method for manufacturing such material that overcomes the deficiencies of the presently known materials and methods for manufacture. In addition to these concerns, such advancements must improve the cushioning capability of the embossed plastic materials used in protective containers by increasing the post-embossing relief height, resilience, durability, and three-dimensional stability of the embossed image. Ideally, the preferred embossed plastic material will also minimize the surface area of plastic in contact with the item stored in the protective container to, in turn, minimize the frictional abrasion acting upon the item, by the plastic material, as the item is inserted and removed from the protective container.